Solid oxide fuel cells fueled by carbonaceous fuels: A thermodynamics-based approach for safe operation and experimental validation

ABSTRACT

Solid Oxide Fuel Cells (SOFCs) can operate with carbonaceous fuels. However, experiments indicate possible carbon deposition or coking on Ni-based anodes. Thermodynamic equilibrium calculations with NASA computer program CEA (Chemical Equilibrium with Applications) for typical SOFC operating temperatures predict graphitic carbon (C(gr)) formation. While fuel humidification eliminates coking, excess steam degrades Ni-based anode, necessitating suitable steam supply for safe operation. Thermodynamic approach is validated using experiments on 25 mm diameter electrolyte-supported NextCell-HP SOFC button cell fueled by H₂ and simulated syngas (CO and H₂). The use of 1 SLPM H₂ (fuel) with 4 SLPM air (oxidant) provides peak power density of ~1000 mW cm⁻². With simulated syngas fuel, cell performance drops. In-situ diagnosis with steam supply to anode suggests carbon deposition based on detection of H₂ and CO in tail gas. Equilibrium analysis suggests carbon-free operation by humidifying simulated syngas (CO:H₂ = 1:3 molar ratio) with ~5% steam by volume, at 973 K and above. Further experiments are conducted on a fresh cell. Simulated syngas (CO:H₂ = 1:3 volumetric ratio) with ~5% steam by volume provides safe cell operation. The study provides a pathway to safely utilize carbonaceous fuels in SOFC by suitable humidification, coupling thermodynamic analyses and experiments.

KEYWORDS:

• Solid oxide fuel cell
• syngas
• hydrogen
• carbon monoxide
• fuel humidification
• carbon deposition

Acknowledgments

The authors thank the Ministry of New and Renewable Energy (MNRE) and Rural Hybrid Energy Enterprises System (RHEES) for funding the research work. The authors thank NFTDC Hyderabad for helping to establish the test rig, Dr. Senthil Kumar and Dr. S. T. Aruna, NAL Bangalore, for the technical discussions related to the research.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the Ministry of New and Renewable Energy India;Rural Hybrid Energy Enterprises System (RHEES).